Beelzebub is a god that was worshiped by the Philistines.  2 Kings 1:1-2, “Now Moab rebelled against Israel after the death of Ahab. 2 And Ahaziah fell through the lattice in his upper chamber which was in Samaria, and became ill. So he sent messengers and said to them, “Go, inquire of Baal-zebub, the god of Ekron, whether I shall recover from this sickness.”

Beelzebub is referenced in Matt 12:24 as the ruler of the demons, “But when the Pharisees heard it, they said, ‘This man casts out demons only by Beelzebul the ruler of the demons.’”  (See also Matt. 10:25; Mark 3:22; Luke 11:15)